Scorpion toxins and defensins

Advances in CT, MR imaging, and catheter angiography provide the radiologist and neurosurgeon with a variety of imaging options for screening, diagnosis, presurgical evaluation, and postoperative monitoring of patients with intracranial aneurysms. Noninvasive imaging techniques have not replaced conventional angiography for the comprehensive evaluation o aneurysms but are effective in screening patients suspected to have an unruptured aneurysm or for preoperative planning in emergency situations that preclude catheter angiography. CT, CT angiography, MR imaging, and MR angiography can all complement the information obtained with catheter angiography in presurgical planning, and the choice of supplemental studies should be individualized. Rotational and intraoperative angiography are problem-solving options used for selected cases at our institution. Continuous improvements in techniques for CT and MR angiography may someday reach the point where surgery can be undertaken on the basis on noninvasive imaging alone, with catheter angiography reserved for endovascular therapy planning and guidance.     

Magnetic resonance imaging based digitally reconstructed radiographs, virtual simulation, and three-dimensional treatment planning for brain neoplasms

Currently, patients with brain neoplasms must undergo both computed tomography (CT) and magnetic resonance (MR) imaging to take advantage of CT's density information and MR's soft tissue imaging capabilities. A method has been developed that allows virtual simulation, digitally reconstructed radiographs (DRRs), and 3-D treatment planning of patients with brain neoplasms to be generated using only one T1-weighted MR data set. DRRs of an anthropomorphic RANDO head phantom were generated using MR and CT imaging. The MR based DRRs provided structural information equivalent to CT based DRRs. The spatial linearity of CT and MR image sets was evaluated by measuring the percent distortion and spatial error. There was no statistical difference in spatial linearity or accuracy between the CT and MR image sets. MR and CT based treatment planning were compared using a variety of different treatment accessories, field sizes, photon energies, and gantry positions. Doses at various points throughout the head phantom were used as comparison points between CT based heterogeneous, CT based homogenous, and MR based homogenous treatment planning of the head phantom. Lithium fluoride thermoluminescent dosimeters were used to verify the dosimetric accuracy of MR based treatment planning by taking measurements at these points. For treatment plans with fields that pass through large air cavities, such as the maxillary sinus, homogenous treatment planning produces unacceptable dosimetric error (2%-4%). For treatment plans with fields that pass through the skull, MR homogenous treatment planning can be used with a dosimetric accuracy of +/- 2%.     

Pyrrolizidine alkaloids from Senecio nevadensis

Residual tumor volume has been considered important in predicting survival following brain surgery. The purpose of this study was to develop a procedure for quantifying pre- and postsurgical brain tumor volumes that is less subjective than the traditional qualitative grading scale still used by surgeons and radiologists to assess extent of resection (such as gross total, subtotal, and partial resection). Pre- and postsurgical magnetic resonance (MR) imaging brain scans on GE Medical System optical disks were transferred to a Macintosh personal computer using a Pioneer optical disk drive subsystem, and the MedVision 1.41 computer software program was used to analyze regions of interest (ROIs) within them for computation of the volume of tumor tissue therein. Because this procedure puts the original MRI (or CT scan) data file for a patient directly into the personal computer, it bypasses the need for scanning and digitizing MR (or CT scan) film images. Between June 1993 and May 1996, pre- and postsurgical volumetric measurements were made in more than 1,000 brain tumor resection cases and 49 radiosurgery cases. The average intra-observer error was estimated to be 1.8%. This method should facilitate the examination of the effects of various therapies on extent of brain tumor resection. The method is fast, is more precise than intraoperative visual assessment of tumor removal or qualitative comparison of pre- and postoperative scans, and it allows the computation of pre- and postsurgical (three-dimensional) volumes of even irregularly shaped tumors.     

Improved activation maps via the elimination of motion effects through time-domain mixing of data in conventional gradient echo functional MRI

To date, most functional imaging centers have relied on ultrafast imaging approaches such as echo-planar imaging (EPI) techniques for acquiring functional brain activation data. These methods require specialized hardware and are not yet installed widely on clinical MR imagers, thus limiting the application of functional MR imaging at many sites. EPI is used to limit motion artifacts and to collect multiple images under different task paradigms in order to distinguish reliably true signal changes from noise. However, it suffers from poor signal to noise ratio because of the high sampling bandwidth employed. This work presents an approach for increasing the efficiency of functional studies that use conventional gradient echo imaging. In this approach, small numbers of image data sets are acquired and recombined to generate composite datasets with minimized motion artifacts. The technique is introduced, and several algorithms for combining the data are explored. A receiver operator characteristic analysis and in vivo studies are performed to examine the efficacy of this approach for improving functional MR imaging studies.     

Low prevalence of the ret/PTC3r1 rearrangement in a series of papillary thyroid carcinomas presenting in Belarus ten years post-Chernobyl

Many neurosurgeons prefer to use intraoperative computed tomographic (CT) scanning, when possible, to check whether there is residual lesion or unexpected bleeding. We report a practical intraoperative CT imaging system using a high-speed CT scanner installed in the operating room along with a digitally controlled neurosurgical operating table. We designed a rail-track system to mobilize the CT gantry. The gantry is fixed onto a motorized carrier that can be moved smoothly on a rail-track embedded in the floor and with a maximum reach of 2.85 m from the room's wall to the operating table. The longitudinal motion of the operating table is easily adjusted by a foot switch from manual control to automatic control directly from the CT scanner's computer like an ordinary CT scanner bed in increments of 2, 5 or 10 mm during CT scanning. Either a carbon-made radiolucent head frame or carbon-made head plate is used as a headrest. Using this CT scanner system, pre- and intraoperative CT scannings were performed on 46 patients with brain tumors, cervical lesions or other intracranial lesions. We could operate on the patient with enough working space between the mobile CT gantry and the operating table for microneurosurgery. We could obtain intraoperative CT imaging of a patient on the operating table while the surgical wound remained open, the surgical drapes kept in place, and the surgical position unchanged, saving time in intraoperative CT scanning and preparation for further surgery when needed. This intraoperative CT imaging system installed in the operating room should be useful for neurosurgery.     

Aldosterone activates the nuclear pore transporter in cultured kidney cells imaged with atomic force microscopy

The 6-years results are described of intraoperative ultrasonic imaging of the brain tumors and are compared with the results of preoperative computerized tomography. On the basis of 169 cases it was shown that the lesions well visible in preoperative CT (with or without contrast) were also well delineated in USG. In cases of presence in CT with or without contrast of extensive isodense or hypodense area, USG could localize in all patients the tumor with suggestion of its morphology. Intraoperative ultrasonic investigation is a valuable method supplementing preoperative diagnostic procedures, facilitating the localization of isomorphic tumors, reducing brain traumatization and making possible control of radical removal of the lesions.     

MR diagnosis of cerebrospinal fluid fistulas using a 3D-CISS sequence

PURPOSE: We compared a new MR method for diagnosis of CSF fistulas with CT cisternography. MATERIAL AND METHODS: In a prospective case study we examined 35 patients with posttraumatic CSF fistulas and compared the results with the intraoperative findings. The MR investigation was performed using a 1.0T whole body MR-system. We used a strongly T2*-weighted 3D-CISS sequence. The examinations were performed in prone position, in patients with severe CSF rhinorrhoea additionally in supine position. RESULTS: The sensitivity and specificity of the MR method (88.9% and 95.1%) is higher compared with CT cisternography (77.8% and 87.8%). The reason for the lower sensitivity of CT compared with MRI are complex fracture systems, involving several paranasal cavities in patients with false positive results in CT cisternography. Reasons for the lower specificity of CT cisternography are false negative results in patients with small dural lesions below 2 mm2. CONCLUSION: Using a new method MRI can detect CSF-fistulas. The MR method is superior to CT cisternography, is noninvasive, the administration of contrast and agent is no longer necessary.     

A novel class of mosquitocidal delta-endotoxin, Cry19B, encoded by a Bacillus thuringiensis serovar higo gene

Construction of computational blood flow models from magnetic resonance (MR) scans of real arteries is a powerful tool for studying arterial hemodynamics. In this report we experimentally determine a lower bound for errors associated with such an approach, and present techniques for minimizing such errors. A known, simple three-dimensional geometry (cylindrical tube) was imaged using a commercial MR scanner, and the resulting images were used to construct finite element flow models. Computed wall-shear stresses were compared to known values and peak errors of 40-60% were found. These errors can be attributed to limited spatial resolution, image segmentation and model construction. A simple smoothing technique markedly reduced these peak errors. We conclude that smoothing is required in the construction of arterial models from in vivo MR images. If used appropriately, such images can be used to construct acceptably accurate computational models of realistic arterial geometries.     

Ultrasonic classification of carotid plaques causing less than 60% stenosis according to ultrasound morphology and events

Carotid plaque morphology studied by ultrasound has been used to classify 3 types of bifurcation plaques, producing less than 60% stenosis on duplex scanning: Type A, the homogeneous, highly echogenic plaque; Type B, the heterogeneous (mainly echogenic, B-1 or mainly echolucent, B-2) plaque; Type C, the complex plaque with irregular surface, echogenic and/or echolucent with calcifications. One hundred asymptomatic subjects in each plaque group were included in a prospective 4-year follow-up study to evaluate clinical events and brain damage by yearly cerebral CT and MR scans. After four years 96 subjects with type A plaque, 89 with type B-1 and 67 with type C plaques completed the study. While there were no clinical events or positive cerebral scans in subjects with type A plaques there was a significantly increasing number of cerebral and vascular events in subjects with plaque B and C type with a zero mortality in the plaque A group, a 2.24% mortality in type B plaques and a significantly higher (p > 0.05) mortality (13.4%) in type C plaques. CT and MR scans revealed brain damage which had been totally asymptomatic with MR detecting a larger number of lesions. Also the number of cerebral lesions observed by CT/MR were significantly greater than the number of recorded clinical episodes. ECG stress test revealed a larger number of asymptomatic coronary disease in the C type plaques. In conclusion ultrasound plaque morphology is linked to different incidences of cerebral and cardiac events, brain damage and asymptomatic coronary disease. Also CT and MR may reveal lesions which do not cause signs or symptoms.     

Value of CT scan and MRI in primary tumors of the ovary

Characterisation of an ovarian mass is of utmost importance in the preoperative evaluation of an ovarian neoplasm. It enables the surgeon to anticipate carcinoma of the ovary before the operation, so that adequate procedures are planned. Although, ultrasonography (US) remains the foremost imaging modality for screening patients with adnexal lesions, computed tomography (CT) recently has proved to be of value in the characterisation and management of tumors of the ovary. Magnetic resonance (MR) imaging has also been shown to have a high degree of diagnostic specificity for certain types of ovarian masses, such as dermoid cysts, and endometriomas. However, the potential of MR imaging to characterize tumors of the ovary has not yet been established. This study assesses the value of MR imaging and CT for the purpose of predicting the malignancy of ovarian lesions, and comparing findings of MR imaging with those of CT.     

A physiological model for motion-stereo integration and a unified explanation of Pulfrich-like phenomena

Many psychophysical and physiological experiments indicate that visual motion analysis and stereoscopic depth perception are processed together in the brain. However, little computational effort has been devoted to combining these two visual modalities into a common framework based on physiological mechanisms. We present such an integrated model in this paper. We have previously developed a physiologically realistic model for binocular disparity computation (Qian, 1994). Here we demonstrate that under some general and physiological assumptions, our stereo vision model can be combined naturally with motion energy models to achieve motion-stereo integration. The integrated model may be used to explain a wide range of experimental observations regarding motion-stereo interaction. As an example, we show that the model can provide a unified account of the classical Pulfrich effect (Morgan & Thompson, 1975) and the generalized Pulfrich phenomena to dynamic noise patterns (Tyler, 1974; Falk, 1980) and stroboscopic stimuli (Burr & Ross, 1979).     

Preoperative instrumental diagnosis in secondary hyperparathyroidism

There is a very high incidence of hyperparathyroidism secondary to chronic renal insufficiency in dialysed patients (67%). When medical therapy can no longer control the evolution of disease, an appropriate surgical strategy must be defined for the clinical case. Instrumental tests play an important role during the preoperative phase in the possible "localisation" of ectopic parathyroids (10% of cases) and the identification of those glands with a more pronounced hyperplastic appearance. The authors examine and describe the most useful tests for a preoperative study, namely ultrasonography, echo-colour Doppler, scintigraphy using a dual tracer and image subtraction, computerised xial tomography (CT), magnetic resonance (MR), digital angiography and intraoperative ultrasonography. In conclusion, it can be said that all the methods examined present similar sensitivity levels for the study of parathyroid, but the combination of more than one technique considerably improves diagnostic accuracy.     

Sphenoethmoidal mucoceles with intracranial extension--three case reports

Three unusual cases of sphenoethmoidal mucoceles with rare intracranial extension are reported. A 64-year-old female presented with a 7-month history of right visual disturbance. Computed tomography (CT) and magnetic resonance (MR) imaging demonstrated a huge mass in the right middle fossa. She underwent right frontotemporal craniotomy. Postoperatively, her proptosis and cranial nerve dysfunction had improved markedly. A 53-year-old female complained of headache, nausea, and dizziness. CT and MR imaging revealed a cystic mass filling the right sphenoid sinus. The cystic lesion was evacuated through the transnasal approach. She was doing well postoperatively and has been asymptomatic. A 39-year-old male complained of headache, vomiting, and right visual disturbance. CT and MR imaging demonstrated a homogeneous mass occupying the sphenoid sinus. Sphenoidotomy exposed the cyst extending superiorly into the anterior cranial fossa. He recovered from the visual disturbances and has been asymptomatic since. MR imaging provides confirmation of the diagnosis of sphenoethmoidal mucocele and is important for preoperative evaluation.     

Accuracy evaluation of fusion of CT, MR, and spect images using commercially available software packages (SRS PLATO and IFS)

PURPOSE: A problem for clinicians is to mentally integrate information from multiple diagnostic sources, such as computed tomography (CT), magnetic resonance (MR), and single photon emission computed tomography (SPECT), whose images give anatomic and metabolic information. METHODS AND MATERIALS: To combine this different imaging procedure information, and to overlay correspondent slices, we used commercially available software packages (SRS PLATO and IFS). The algorithms utilize a fiducial-based coordinate system (or frame) with 3 N-shaped markers, which allows coordinate transformation of a clinical examination data set (9 spots for each transaxial section) to a stereotactic coordinate system. The N-shaped markers were filled with fluids visible in each modality (gadolinium for MR, calcium chloride for CT, and 99mTc for SPECT). The frame is relocatable, in the different acquisition modalities, by means of a head holder to which a face mask is fixed so as to immobilize the patient. Position errors due to the algorithms were obtained by evaluating the stereotactic coordinates of five sources detectable in each modality. RESULTS: SPECT and MR position errors due to the algorithms were evaluated with respect to CT: deltax was < or = 0.9 mm for MR and < or = 1.4 mm for SPECT, deltay was < or = 1 mm and < or = 3 mm for MR and SPECT, respectively. Maximal differences in distance between estimated and actual fiducial centers (geometric mismatch) were in the order of the pixel size (0.8 mm for CT, 1.4 mm for MR, and 1.8 mm for SPECT). In an attempt to distinguish necrosis from residual disease, the image fusion protocol was studied in 35 primary or metastatic brain tumor patients. CONCLUSIONS: The image fusion technique has a good degree of accuracy as well as the potential to improve the specificity of tissue identification and the precision of the subsequent treatment planning.     

Registration of MR and SPECT without using external fiducial markers

The aim of our work is to present, test and validate an automated registration method used for matching brain SPECT scans with corresponding MR scans. The method was applied on a data set consisting of ten brain IDEX SPECT scans and ten T1- and T2-weighted MR scans of the same subjects. Of two subjects a CT scan was also made. (Semi-) automated algorithms were used to extract the brain from the MR, CT and SPECT images. Next, a surface registration technique called chamfer matching was used to match the segmented brains. A perturbation study was performed to determine the sensitivity of the matching results to the choice of the starting values. Furthermore, the SPECT segmentation threshold was varied to study its effect on the resulting parameters and a comparison between the use of MR T1- and T2-weighted images was made. Finally, the two sets of CT scans were used to estimate the accuracy by matching MR to CT and comparing the MR-SPECT match to the SPECT-CT match. The perturbation study showed that for initial perturbations up to 6 cm the algorithm fails in less than 4% of the cases. A variation of the SPECT segmentation threshold over a realistic range (25%) caused an average variation in the optimal match of 0.28 cm vector length. When T2 is used instead of T1 the stability of the algorithm is comparable but the results are less realistic due the large deformations. Finally, a comparison of the direct SPECT-MR match and the indirect match with CT as intermediate yields a discrepancy of 0.4 cm vector length. We conclude that the accuracy of our automatic matching algorithm for SPECT and MR, in which no external markers were used, is comparable to the accuracies reported in the literature for non-automatic methods or methods based on external markers. The proposed method is efficient and insensitive to small variations in SPECT segmentation.     

Potential pitfalls in the work-up and diagnosis of choanal atresia

To increase an awareness of the developmental anatomy of the nasal cavity as it applies to the radiologic work-up of choanal atresia and frontoethmoidal cephaloceles, we report two cases that demonstrate potentially serious imaging pitfalls. Two neonates with nasopharyngeal obstruction were imaged with CT and MR. Both patients had surgically proved bilateral bony choanal atresia. In addition to choanal atresia, CT showed a radiolucent, or nonossified cribriform plate and mucoid secretions within the nasal fossa, adjacent to the cribriform plate, which approximated the attenuation of brain parenchyma. In one of the patients, a preoperative diagnosis of nasopharyngeal encephalocele resulted in surgical exploration. At surgery, however, the cartilaginous cribriform plate was found to be intact.     

Development of a frameless and armless stereotactic neuronavigation system with ultrasonographic registration

OBJECTIVE: We have developed a frameless stereotactic neuronavigation system that allows navigation during neurosurgical procedures through an image formed from integrating ultrasonography and preoperative magnetic resonance (MR) imaging and/or x-ray computed tomography. METHODS: The system consists of a ultrasound imaging scanner, a workstation with an image capture board, and an ultrasonic tracking sensor with a 5-MHz ultrasonographic transducer. The ultrasonic tracking sensor measures the position and orientation of the ultrasonographic transducer. The oblique plane of the MR/computed tomographic image corresponding to the ultrasound image is then displayed on the workstation monitor. A three-dimensional computer graphic representation of the integrated image is also reported as a preliminary test. For the patient-image registration, the coordinates of digitized and imaged markers on a specifically developed reference frame are used. The reference frame is noninvasive because it is not bolted but only fastened to the patient's head with silicon. RESULTS: Based on the findings from the clinical application of the system in three cases, the system was advantageous because of the surgical procedures could be controlled by intraoperative ultrasonography as well as by preoperative MR/computed tomographic images. Missing parts in the ultrasonogram were supplemented with preoperative MR/computed tomographic images. At other times, spatial positioning and visualization by ultrasonography were useful for identifying anatomical objects in the image. CONCLUSION: This preliminary study of the frameless integration of ultrasonography into stereotactic space demonstrated its clinical usefulness. We believe that the concept of pre- and intraoperative image-guided surgery presented here will find increasing use in the future.     

Diffusion-weighted MR imaging of acute cerebral ischemia

Diffusion-weighted MR imaging has been used in studies on experimental animal models and on patients with acute cerebral ischemia. Compared with CT and conventional MR techniques, diffusion-weighted imaging can provide earlier and more precise detection of the location and the extent of an ischemic lesion during the critical first few hours after the onset of stroke. Quantitative apparent diffusion coefficient (ADC) mapping of the brain water can also be carried out by recording a series of diffusion-weighted images with different amplitudes of the displacement encoding gradients. ADC maps can provide important information about the extra- and intracellular water homeostasis. ADC reduction of the tissue water is one of the early signals of the pathophysiological cascade resulting from ischemic tissue injury. Diffusion MR imaging has become a valuable tool in stroke research. It may also prove a valuable tool in monitoring the efficiency of therapeutic effects in stroke patients. It is our intention to provide an overview of the recent development in this area with emphasis on the diffusion-weighted MR techniques, and to discuss the possible underlying biophysical mechanisms responsible for the contrast of diffusion-weighted imaging.     

Risk analysis of linear accelerator radiosurgery

PURPOSE: To evaluate the toxicity of stereotactic single-dose irradiation and to compare the own results with already existing risk prediction models. METHODS AND MATERIALS: Computed tomography (CT) or magnetic-resonance (MR) images, and clinical data of 133 consecutive patients treated with linear accelerator radiosurgery were analyzed retrospectively. Using the Cox proportional hazards model the relevance of treatment parameters and dose-volume relationships on the occurrence of radiation-induced tissue changes (edema, localized blood-brain barrier breakdown) were assessed. RESULTS: Sixty-two intraparenchymal lesions (arteriovenous malformation (AVM): 56 patients, meningioma: 6 patients) and 73 skull base tumors were selected for analysis. The median follow-up was 28.1 months (range: 9.0-58.9 months). Radiation-induced tissue changes (32 out of 135, 23.7%) were documented on CT or MR images 3.6-58.7 months after radiosurgery (median time: 17.8 months). The actuarial risk at 2 years for the development of neuroradiological changes was 25.8% for all evaluated patients, 38.4% for intraparenchymal lesions, and 14.6% for skull base tumors. The coefficient: total volume recieving a minimum dose of 10 Gy (VTREAT10) reached statistical significance in a Cox proportional hazards model calculated for all patients, intraparenchymal lesions, and AVMs. In skull base tumors, the volume of normal brain tissue covered by the 10 Gy isodose line (VBRAIN10) was the only significant variable. CONCLUSIONS: These results demonstrate the particular vulnerability of normal brain tissue to single dose irradiation. Optimal conformation of the therapeutic isodose line to the 3D configuration of the target volume may help to reduce side effects.     

MR image-guided portal verification for brain treatment field

PURPOSE: To investigate a method for the generation of digitally reconstructed radiographs directly from MR images (DRR-MRI) to guide a computerized portal verification procedure. METHODS AND MATERIALS: Several major steps were developed to perform an MR image-guided portal verification procedure. Initially, a wavelet-based multiresolution adaptive thresholding method was used to segment the skin slice-by-slice in MR brain axial images. Some selected anatomical structures, such as target volume and critical organs, were then manually identified and were reassigned to relatively higher intensities. Interslice information was interpolated with a directional method to achieve comparable display resolution in three dimensions. Next, a ray-tracing method was used to generate a DRR-MRI image at the planned treatment position, and the ray tracing was simply performed on summation of voxels along the ray. The skin and its relative positions were also projected to the DRR-MRI and were used to guide the search of similar features in the portal image. A Canny edge detector was used to enhance the brain contour in both portal and simulation images. The skin in the brain portal image was then extracted using a knowledge-based searching technique. Finally, a Chamfer matching technique was used to correlate features between DRR-MRI and portal image. RESULTS: The MR image-guided portal verification method was evaluated using a brain phantom case and a clinical patient case. Both DRR-CT and DRR-MRI were generated using CT and MR phantom images with the same beam orientation and then compared. The matching result indicated that the maximum deviation of internal structures was less than 1 mm. The segmented results for brain MR slice images indicated that a wavelet-based image segmentation technique provided a reasonable estimation for the brain skin. For the clinical patient case with a given portal field, the MR image-guided verification method provided an excellent match between features in both DRR-MRI and portal image. Moreover, target volume could be accurately visualized in the DRR-MRI and mapped over to the corresponding portal image for treatment verification. The accuracy of DRR-MRI was also examined by comparing it to the corresponding simulation image. The matching results indicated that the maximum deviation of anatomical features was less than 2.5 mm. CONCLUSION: A method for MR image-guided portal verification of brain treatment field was developed. Although the radiographic appearance in the DRR-MRI is different from that in the portal image, DRR-MRI provides essential anatomical features (landmarks and target volume) as well as their relative locations to be used as references for computerized portal verification.